Reflow soldering is the most common method of attaching surface mount components to a printed circuit board (PCB) in a typical lead-free surface mount technology (SMT) assembly line. In reflow soldering, a solder paste (a sticky mixture of powdered solder and flux) is used to stick electrical components to their electrically conductive contact pads on the PCB. The entire PCB assembly (PCBA) is then heated in a controlled environment to melt the solder, followed by cooling to solidify and permanently connect the joint. Heating may be accomplished, for example, by passing the assembly through a reflow oven or under an infrared lamp. Several such stages may be needed to completely assemble a complex PCBA. Several such stages typically entail heating the work piece to a maximum temperature of about 260° C. (500° F.) for about 10 seconds. Other high-stress SMT manufacturing line processes and environments include BGA/CSP rework, which heats the work piece to about 150° C. when it is in close proximity to the BGA; and the location of the BGA to a maximum temperature of about 260° C. (500° F.) for about 10 seconds, wave/selective wave soldering, which heats the work piece to about 120° C. where the barcode labels are expected; and aqueous cleaning, which takes place at about 70° C. (160° F.). Thus, reflow soldering generally involves the most hostile environment a PCBA experiences in an SMT assembly line, so any component that can withstand multiple reflow soldering stages can be expected to tolerate well anything else the rest of the assembly line requires.
Radio frequency identification (RFID) technology is sometimes used to track PCBs through the assembly line. RFID components and systems are known that can withstand multiple reflow soldering stages and continue to function consistently and accurately. Such an RFID system generally includes an RFID package that contains a silicon based integrated circuit (IC, or “chip”) for wireless communication functionality, electrically coupled to an RFID antenna. Of course, the RFID package must be made of material and have a structure suitable to withstand solder reflow process temperatures as well as shield the internal systems of the component from radio frequency interference and catastrophic damage from parasite signals from other components on the board or from the environment other than those intended by the user to communicate with the internal systems of the component. Such a package may take the form of an SMT component mounted on a PCB. Alternatively, the RFID elements may be mounted directly on the PCB as a bare die; or a combination RFID solution that includes both may be used. For example, FIG. 1 shows an exemplary RFID chip 110 coupled to an RFID antenna 120. As shown, the antenna elements are co-planar with the ground plane of the PCB 130 and were formed when the PCB was manufactured, and the RFID chip 110 was mounted on the board at a later time, such as after the PCB is introduced into an SMT assembly line.
Such SMT process compatible RFID solutions can be coupled to PCBs to track them through the PCBA manufacturing process. Thereafter, the completed PCBA is generally incorporated into a product. As the product is being assembled, after the PCBA is incorporated its RFID chip can also be used to track the product through the rest of its manufacturing process, as well as its boxing and shipping processes. In some cases, an RFID chip may be part of the bill of materials (BOM) of a PCBA to provide a required a design function, such as payment or data transfer. If so, it may be possible to also use that chip for tracking. Otherwise RFID components may be specifically designed and included on the board just for tracking.
There will often be some time between the PCB being placed at the beginning of the assembly line until the RFID is added, during which time RFID cannot be used to track the PCB because it hasn't been added yet. To track the PCB from the beginning of the line, a barcode label may be added to the board before or at the time it is loaded on the SMT line. RFID labels with printable surfaces on which barcodes can be printed onsite are available, but they cannot withstand anything remotely close to reflow temperatures, and so cannot be used in an SMT assembly line that includes reflow soldering. High temperature RFID barcode tags also exist that can withstand reflow temperatures, but they are bulky, expensive, and cannot be printed onsite.
Manufacturers are also working toward an RFID solution in which an RFID chip is embedded inside the PCB. An illustrative example of this approach is shown in FIG. 2. As shown, RFID package (1) is inserted into a cavity formed in the PCB (2), to provide a PCB with RFID (3). Illustratively, the cavity in the PCB may be formed during or after the board is manufactured, and the RFID package would be mounted in the board at a later time, such as after the PCB is introduced into an SMT assembly line. When such a solution becomes available, the embedded RFID could be used to track the PCB after the point in the assembly line where the RFID chip (1) is mounted in the board or prior to it being introduced in the SMT line if it is embedded by the PCB fabricator.
Whenever an RFID solution is to be included in or on a PCB, it must be provided for in the original design of the PCB assembly. That is, an RFID solution cannot be added after the PCB is manufactured, at least because the PCB wasn't designed to accommodate it and there won't be any space on the PCB for it. This will also be true for embedded RFID when it becomes available. Moreover, embedding an RFID chip in a fully functional complex PCB board is still a few years away from being a commercially viable, robust technology with accepted design rules, proven cost benefits, and demonstrated reliability. Overcoming these challenges cannot be accomplished simply by modifying existing PCB board designs, but will require significant new investment and development.